ya it may have been a faulty grenade (never heard of one before) but i doubt it. it probably took so long to go off because once gas is filled in room temperature and then suddenly borught to -7c (stupid canadian weather) the gas majorly gets to be a smaller amount which means that it wont have the push force it needs to go off at the proper time because not enough gas is pushing on it for the cylinder to move upwards. another problem i realized that u did was not lubricate it properly. this grenade comes dry (without any silicon oil already in it) it is recomended that you completely take down the grenade and lubricate every part demonstrated on this video
YouTube - Reassembling the AI Tornado Grenade
hope this helps =)